For Sentinel-2, added support for parallax test to remove false cloud in bright (typically
urban) areas, as per Frantz (2018). Optional, defaults to off. Thanks to Vincent Schut
for assistance in kicking that across the line.

For Sentinel-2, added command line switch to directly use the SAFE directory as
provided by ESA, to avoid the need to manually stack up the individual bands externally.

For Sentinel-2, turn off the (cloud prob > 99%) test, as suggested by Zhu (2015). It is
in effect for Landsat.